fell remained in situ—the wind tore it away in sheets and streams. It will be remembered, too, that no inconsiderable amount passes off by evaporation. If other pits had been sunk to the north and to the south of the pass, we should probably have found in them a greater depth of snow between each of the horizontal layers of pure ice. This is mere conjecture, and it may be taken for what it is worth. It is more important to note—1. (a) That the fine layers or strata of pure ice were numerous towards the surface; (b) disappeared as we descended; (c) and that the lower strata were, upon the whole, much thicker than those towards the surface. 2. That the thickness of these strata of pure ice amounted to nearly one-tenth of the mass that we were able to penetrate. 3. That, below the depth of 15 feet, vertical glacification began to show itself. Upon each of these subjects I will now venture to offer a few remarks.
1 (a.) The fine horizontal layers or strata of pure ice were numerous towards the surface. All of these layers had been formed by weathering at the surface. It is usual, even during the winter, for considerable periods of fine weather to succeed heavy snow-falls; and in these periods the surface of the snow is alternately melted and refrozen, and, at length, is glazed with a crust or film of pure ice. This, when covered up by another snow-fall, and exposed as in the section, appears as a bluish horizontal line drawn through the whiter mass. The snow between any two of these layers (near the surface) did not therefore represent a year's snow, but it was the remnant, and only the remnant, of a considerable fall, between whose deposition, and that of the next stratum above, a considerable interval of time had probably elapsed.
(b.) The fine strata disappeared as we descended. I imagine that this was a result of pressure from the superincumbent mass, but I leave to others to show the exact manner in which these finer strata were got rid of. Is it possible to liquefy by steady pressure a plate of ice (say, one-tenth of an inch in thickness) placed in the interior of a mass of snow, without liquefaction of the snow ?
(c.) The lower strata of pure ice were, upon the whole, thicker than those towards the surface. This, doubtless, was a result of vertical pressure. The strata grew under pressure. But why should some grow and others disappear? I presume that the finest ones disappear, and that the stouter ones grow. Can it be shown experimentally that it is possible to liquefy by steady pressure a fine plate of ice placed in the interior of a mass of snow, and at the same time, under the same conditions, to thicken another and stouter plate of ice?
2. These horizontal strata of pure ice amounted in the aggregate to nearly one-tenth of the thickness of the mass that we penetrated. It was perfectly well known prior to 1866 that the upper snows (which give birth to glaciers) were pervaded with strata of pure ice, and a host of observers had written before that date upon stratification of snow and of glacier. It may be questioned, however, whether any had an idea of the very important amount of glacification that is effected by superficial weathering, and subsequent thickening of the strata through vertical pressure. A search through the works of the principal writers on glaciers has failed to show me that any person imagined that one-tenth of the mass, or anything like that amount, was composed of strata of pure ice.
